Biological catalysis and energy transduction often rely on rapid charge transport over great distances (>20 E) within and between proteins. Many redox enzymes, especially those involved in the activation of strong chemical bonds (e.g. O-H, O=O, C-H), also require charge transport at high potentials. The combination of long-range and high potential charge transport places strict design requirements on enzyme scaffolds that carry out these reactions. Numerous redox enzymes use the redox active amino acids tryptophan (W) and tyrosine (Y) as redox 'way stations' to break long-range charge transport into shorter electron tunneling steps. This is known as 'hopping.' This research will examine the factors that influence hopping through Y in artificial blue-copper azurin model systems. All of these systems consist of a tyrosine residue situated between the azurin-CuI center and a (protein) surface attached photosensitizer. Our azurin models are specifically designed to account for the proton transfer that must accompany redox reactions of tyrosine. Introduction of an acidic tyrosine, 3-nitro-tyrosine (Aim 1), will allow for studies of hopping via tyrosinate, where proton transfer is not important. An important structural motif in biological Y-hopping systems is the positioning of a basic moiety near the phenolic proton of Y, which accepts the proton upon Y oxidation. A series of mutant azurins will be produced and studied where proton accepting groups, such as aspartate or histidine, are situated near Y (Aim 2). It is expected that the position of these bases will facilitate reversible electron transfer via tyrosine. By using the design criteria gleaned from Aims 1 and 2, azurin models where ultra-long-range charge transport (> 30 E) occurs through Y will be explored (Aim 3). PUBLIC HEALTH RELEVANCE: Reduction and oxidation (redox) pathways that involve the amino acid tyrosine are vital in a wide array of metabolic processes. Numerous diseases are associated with failure, disruption or malfunction of redox pathways. Elucidation of the fundamental factors that control biological redox chemistry of tyrosine will lead to deeper understanding of disease mechanisms and inform the development of new therapies.